Effective enrichment and separation of three flavonoids from Ohwia caudata (Thunberg) H. Ohashi using magnetic layered double hydroxide/ZIF-8 composites and pCEC

Abstract

In this study, Fe3O4@ZnCr–layered double hydroxide/zeolitic imidazolate frameworks-8 (MLDH/ZIF-8) magnetically functionalized composites were synthesized by co-precipitation and in situ growth based on the advantages of LDHs and ZIF-8 using Fe3O4 nanoparticles as a magnetic substrate to obtain adsorbents with excellent performance. Moreover, the composite was used for the efficient enrichment of flavonoids in Chinese herbal medicines. The internal structures and surface properties were characterized by SEM, Fourier transform infrared spectroscopy, X-ray diffraction and so on. MLDH/ZIF-8 exhibited a large specific surface area and good paramagnetic properties. The MLDH/ZIF-8 magnetic composite was used as a magnetic solid-phase extraction (MSPE) adsorbent, and a MLDH/ZIF-8 MSPE–pressurized capillary electrochromatography coupling method was developed for the separation and detection of flavonoids (luteolin, kaempferol and apigenin) in a sample of the Chinese herb Ohwia caudata (Thunberg) H. Ohashi. The relevant parameters affecting the extraction efficiency were optimized to determine the ideal conditions for MSPE. 5 mg of adsorbent in sample solution at pH 6, vortex extraction for 5 min, elution with 1.5 mL of ethyl acetate for 15 min. The method showed good linearity in the concentration range of 3–50 μg mL−1 with correlation coefficients of 0.9934–0.9981, and displayed a relatively LODs of 0.07–0.09 μg mL−1. The spiked recoveries of all analytes ranged from 84.5% to 122.0% with RSDs (n=3) between 4.5% and 7.7%. This method is straightforward and efficient, with promising potential in the separation and analysis of active ingredients in various Chinese herbal medicines.